The present invention relates to a method and device for assessing the viability, in other words vitality, of intact teeth, and more particularly to a device and method for assessing the amount of blood in a tooth of a patient based on the ratio of transmission of light of at least two wavelengths.
A well known problem in conventional dentistry is the determination of changes in vitality of a tooth which remains intact in the mouth of a patient. As a patient ages, a tooth can gradually or suddenly lose its circulation of blood, and at some point can essentially become a dead tooth. Although such a dead tooth can continue to function as an intact tooth indefinitely, on the other hand, problems can arise once the tooth loses its vitality and approaches the status of being dead. In any case, it is of interest to the dentist, and certainly to his patient, to be aware of any changes in tooth vitality, even when the change is occurring slowly.
A current clinical method of assessing tooth vitality is to electrically stimulate the tooth, to see if the patient can sense the stimulation. This method has two disadvantages. First, it is limited to the patient's ability to localize the sensation, and second, the presence of irritability does not necessarily indicate that the tooth has intact circulation. Other prior art has involved the use of light for detecting the condition of teeth or for detecting the presence of blood in human tissue. For instance, Alfano in U.S. Pat. No. 4,290,433 (and see also U.S. Pat. No. 4,479,499) teaches a method and apparatus for detecting caries in teeth using the relative luminescence of teeth at two wavelengths. This involves illuminating a surface of a tooth with short wavelength visible light, and collecting the light received back from the surface at longer wavelengths. The spectrum of the received light depends on the extent of the caries or decay which is present on the surface of the tooth. Wilber in U.S. Pat. No. 4,407,290 involves detecting in human tissue a pulse of a varying constituent of flowing blood. Others have sought to measure fluorescence illuminisence in tissue or in the breath of a person (U.S. Pat. Nos. 3,811,777, 3,725,658 and 4,178,917), or to measure optical density in tissue to estimate its dimensions (U.S. Pat. No. 3,648,685, 3,674,008), to map an image of the surface of an object (U.S. Pat. No. 4,564,355, 4,575,805, 4,170,987), or to measure surface color (U.S. Pat. No. 3,709,612, 2,437,916). Prior art efforts in the fields of egg-candeling have addressed the problem of detecting blood in eggs, and pulse oximetry has involved use of different wavelengths for determining relative amounts of oxyhemoglobin and reduced hemoglobin in blood. Photo-plethsmography involves techniques for assessing blood flow. Such prior art is directed to entirely different fields of use and involves determination of different physical properties using different devices and methods as compared to the present invention. None of these prior art techniques involve devices or methods which are available for or suggest assessing viability of intact teeth.